A method of allotting the signal links and routing the signal messages in the signalling transfer points of a common channel signalling system which are level type signalling transfer points for carrying out message transfer functions based on the common channel signalling No. 7 protocol of the ITTCC. Each signalling transfer point includes a signalling link selection value composed of a number of bits, signal data links, signal links, signal network functions, clusters and groups, connected in such a manner that a signalling transfer point includes a certain number of signal network functions, each signal network function including a certain number of signal links, each signal link being connected to one signal data link. The signalling transfer point includes a number of clusters of signal links (equal to the number of signal network functions) grouped in a plurality of clusters (equal to the number of signal links). In this system, if a level has a malfunction, replacement levels are available, and the determination as to which cluster has the replacing level can be easily made. As a result, it is always possible to carry out the functions of the signalling transfer point, so long as all the signal network functions are not out of order simultaneously, or at least as long as all the signal links or all the signal data links are not out of order simultaneously.